Java8 de interfaz de colectores

corriente java8 en funcionamiento, en el medio de la terminal y operación de funcionamiento, esta realización también dijo que las operaciones de reducción principales del cobro revertido, operación trampa, como las operaciones de reducción más altas;

Mira debajo de la corriente de la operación de cobro revertido

	<R> R collect(Supplier<R> supplier,BiConsumer<R, ? super T> accumulator,BiConsumer<R, R> combiner);
	<R, A> R collect(Collector<? super T, A, R> collector);

La primera, se pasa a un método abstracto tres parámetros,

La segunda operación colectores recogen sólo una mirada bajo los parámetros de flujo en la clase de fábrica estática, y en esta clase de fábrica estática, la mayor parte del método se dan cuenta tres parámetros se denominan, se encuentran casi toda nuestra diaria operación, por lo tanto, nos fijamos en esta clase de fábrica estática, que logró;



a través de la práctica de código lo

package com.meinergy.vppd.business.api.test;
 
import java.util.ArrayList;
import java.util.Comparator;
import java.util.IntSummaryStatistics;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.Set;
import java.util.function.Function;
import java.util.stream.Collectors;
 
import org.junit.Test;
 
public class TestJava8 {
    public static List<Emp> list = new ArrayList<>();
    static {
        list.add(new Emp("上海", "小名", 17));
        list.add(new Emp("北京", "小红", 18));
        list.add(new Emp("深圳", "小蓝", 19));
        list.add(new Emp("广州", "小灰", 20));
        list.add(new Emp("杭州", "小黄", 21));
        list.add(new Emp("贵阳", "小白", 22));
    }
 
    @Test
    public void test1() {
        // 转list
        List<String> names = list.stream().map(emp -> emp.getName()).collect(Collectors.toList());
        // 转set
        Set<String> address = list.stream().map(emp -> emp.getName()).collect(Collectors.toSet());
        // 转map，需要指定key和value，Function.identity()表示当前的Emp对象本身
        Map<String, Emp> map = list.stream().collect(Collectors.toMap(Emp::getName, Function.identity()));
        // 计算元素中的个数
        Long count = list.stream().collect(Collectors.counting());
        // 数据求和 summingInt summingLong，summingDouble
        Integer sumAges = list.stream().collect(Collectors.summingInt(Emp::getAge));
        // 平均值 averagingInt,averagingDouble,averagingLong
        Double aveAges = list.stream().collect(Collectors.averagingInt(Emp::getAge));
 
        // 综合处理的，求最大值，最小值，平均值，求和操作
        // summarizingInt，summarizingLong,summarizingDouble
        IntSummaryStatistics intSummary = list.stream().collect(Collectors.summarizingInt(Emp::getAge));
        System.out.println(intSummary.getAverage());// 19.5
        System.out.println(intSummary.getMax());// 22
        System.out.println(intSummary.getMin());// 17
        System.out.println(intSummary.getSum());// 117
 
        // 连接字符串,当然也可以使用重载的方法，加上一些前缀，后缀和中间分隔符
        String strEmp = list.stream().map(emp -> emp.getName()).collect(Collectors.joining());
        String strEmp1 = list.stream().map(emp -> emp.getName()).collect(Collectors.joining("-中间的分隔符-"));
        String strEmp2 = list.stream().map(emp -> emp.getName()).collect(Collectors.joining("-中间的分隔符-", "前缀*", "&后缀"));
        System.out.println(strEmp);// 小名小红小蓝小灰小黄小白
        // 小名-中间的分隔符-小红-中间的分隔符-小蓝-中间的分隔符-小灰-中间的分隔符-小黄-中间的分隔符-小白
        System.out.println(strEmp1);
        // 前缀*小名-中间的分隔符-小红-中间的分隔符-小蓝-中间的分隔符-小灰-中间的分隔符-小黄-中间的分隔符-小白&后缀
        System.out.println(strEmp2);
        // maxBy 按照比较器中的比较结果刷选 最大值
        Optional<Integer> maxAge = list.stream().map(emp -> emp.getAge())
                .collect(Collectors.maxBy(Comparator.comparing(Function.identity())));
        // 最小值
        Optional<Integer> minAge = list.stream().map(emp -> emp.getAge())
                .collect(Collectors.minBy(Comparator.comparing(Function.identity())));
        System.out.println("max:" + maxAge);
        System.out.println("min:" + minAge);
 
        // 归约操作
        list.stream().map(emp -> emp.getAge()).collect(Collectors.reducing((x, y) -> x + y));
        list.stream().map(emp -> emp.getAge()).collect(Collectors.reducing(0, (x, y) -> x + y));
        // 分操作 groupingBy 根据地址，把原list进行分组
        Map<String, List<Emp>> mapGroup = list.stream().collect(Collectors.groupingBy(Emp::getAddress));
        // partitioningBy 分区操作 需要根据类型指定判断分区
        Map<Boolean, List<Integer>> partitioningMap = list.stream().map(emp -> emp.getAge())
                .collect(Collectors.partitioningBy(emp -> emp > 20));
 
    }
 
    static class Emp {
        private String address;
 
        private String name;
 
        private Integer age;
 
        public Emp() {
 
        }
 
        public Emp(String address) {
            this.address = address;
        }
 
        public Emp(String name, Integer age) {
            this.name = name;
            this.age = age;
        }
 
        public Emp(String address, String name, Integer age) {
            super();
            this.address = address;
            this.name = name;
            this.age = age;
        }
 
        public String getAddress() {
            return address;
        }
 
        public void setAddress(String address) {
            this.address = address;
        }
 
        public String getName() {
            return name;
        }
 
        public void setName(String name) {
            this.name = name;
        }
 
        public Integer getAge() {
            return age;
        }
 
        public void setAge(Integer age) {
            this.age = age;
        }
 
        @Override
        public String toString() {
            return "Emp [address=" + address + ", name=" + name + ", age=" + age + "]";
        }
 
    }
}